Elucidating metabolic tuning of mixed purple phototrophic bacteria biofilms in photoheterotrophic conditions through microbial photo-electrosynthesis

Abstract

Reducing greenhouse gas emissions is critical for humanity nowadays, but it can be beneficial by developing engineered systems that valorizeCO2 into commodities, thus mimicking nature’s wisdom. Purple phototrophic bacteria (PPB) naturally accept CO2 into their metabolismas a primary redox sink system in photo-heterotrophy. Dedicated use of this feature for developing sustainable processes (e.g., through negative-emissions photo-bioelectrosynthesis) requires a deep knowledge of the inherent metabolic mechanisms. This work provides evidence of tuning the PPB metabolic mechanisms upon redox stressing through negative polarization (−0.4 and −0.8 V vs. Ag/AgCl) in photo-bioelectrochemical devices. A mixed PPB-culture upregulates its ability to capture CO2 from organics oxidation through the Calvin-Besson-Bassam cycle and anaplerotic pathways, and the redox imbalance is promoted to polyhydroxyalkanoates production. The ecological relationship of PPB with mutualist bacteria stabilizes the system and opens the door for future development of photobioelectrochemical devices focused on CO up-cycling.